Piezo-electric loud speaker



Feb. 23 1926. 1,574,302

A. M. NI'COLSON PIE'ZO ELECTRIC LOUD SPEAKER Filed Dec. 31, 1923 f7} .35% Z /5 m /3 //z fimznfan ,4/e/m/7derM/W6'0/s0 Z y Ah} Patented Feb. 23,1926.

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ALEXANDER M. NICOLSON, OFNEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRICCOMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PIEZO-ELECTRIC LOUD SPEAKER.

Application filed December 31, 1923. Serial No. 683,643.

To all whom it may concern:

Be it known that I, ALEXANDER M. NICOL- SON, a subject of the King ofGreat Britain,

residing at New York, in the county of New York and State of New York,have invented certain new and useful Improvements in Piezo-Electric LoudSpeakers, of which the following is a full, clear, concise, and exactdescription.

This invention relates to transforming one form of energy intoanotherwhere one of the forms of energyis the energy of electric current wavesand especially where the other form of energy is the energy of 1 soundwaves.

An object of the invention is an efficient and durable means foraccomplishing such transformation, either of electrical energy tomechanical energy or vice versa, and especially an efficient and durablepiezo-electric loud speaking telephone receiver capable of accuratelyreproducing voice current waves as sound waves of the same form.

In the form of the invention specifically shown and described herein forpurposes of illustration, a piezo-electric crystal has extending throughit and protruding from its walls an internal electrode, and theprotruding parts of the electrode are used to 80 securely and rigidlyfasten the crystal in a band-shaped frame, and also to securely andrigidly fasten the crystal to an arm or plate which transmits elasticvibrations of the crystal to a diaphragm or the like. 86 Plates closethefront and back of the frame, and means extending through one of theplates connects the tone arm and the diaphragm, which is preferably afibrous conical diaphragm having a free periphery. The material, formand mass of the frame are preferably such that it efficiently refleetsthe elastic vibrations of the crystal, so that the vibrations areefliciently transmitted to the diaphragm. Preferably, a base supportsthe frame in such position that a horizontal plane through the. apex ofthe diaphragm would pass between its axis and the lowest point on itsperiphery, so that the base need not be tall in order to bring thelowest part ofthediaphragm higher than the lowest part of the base. Atube containing water or Rochelle salt solution for moistening theinterior of the crystal may penetrate the crystal and be carried by Feltor the like may fill the space between the crystal and the frame and itsfront and back closure plates, to prevent production of undesiredsounds.

In the drawing, Fig. 1 is a side elevation of a loud speaker embodyingthe invention; Fig. 2 is a front View of the device, with the diaphragmremoved; and Fig. 3 is a front view of the device, with both thediaphragm and the base removed, and with the crystal and its frame in avertical position.

The loud-speaker comprises a base 5, a frame 6 mounted or supported onthe base, a pieZo-crystal 7 mounted in the frame, and a diaphragm 8vibrated by the crystal. The crystal is preferably of the type disclosedin Fig. 8 or Fig. 12 of my article on the Piezo-electric effect in thecomposite R0- chelle salt crystal, Proceedings of the American Instituteof Electric Engineers, November 1919, page 1315, and is provided with agirdle-electrode 9 similar to the girdle-electrode shown in thosefigures; but the cr stal 7 is provided with an internal electro e 10instead of with the basal lane electrodes shown in said Fig. 12. T eelectrode 10 is shown by way of example as a bolt passing through thebottom of frame 6, through the crystal 7 in the direction of theprincipal axis of the crystal, through the top of the frame, and througha nut 11 at the top of the frame. electrical connection with the framewhich may be of electrically conducting material, for instance castiron. The lower basal plane of the crystal is preferably cemented to theframe. The electrode 10 also passes through a torsion arm or plate 12,for example, of steel or the like,,which is clamped against the topbasal plane of the crystal by means of a nut 13 on the bolt 10. Theplate 12 may also be cemented to the top basal plane of the crystal. Alead 15 is taken off from a point on frame 6 or from some other point inelectrical connection with electrode 10; and a lead 16 is taken off fromthe girdle electrode 9. To insert the electrode 10 in the crystal, ahole may be drilled in the crystal, the electrode placed in the hole,and conducting material, such for example as tinfoil or graphite (notshown), tamped around the electrode to insure good Thus, the electrode10 is in electrical connection between the crystal and the electrode; orthe crystalv may be grown about the electrode as described inmy ;2t5entNo. 1,562,57 8, granted November 24,

The diaphra diaphragm of brous material, for example, paper or the like,and has its apex .rigidly attached to one end 18 of the torsion arm 12so that vibratory elastic twisting of crystal 7 about its principal axiswill vibrate the apex of the diaphragm in the direction of the axis ofthe diaphragm. I

A tube of glass or the like, containing water,'Rochelle salt solution orthe like for moistening the interior of the crystal may be carried bythe crystal. Preferably one end of the tube is inserted in the crystalso as to penetrate to substantially the center 01 the crystal and theother end of the tube is sealed. The part of the tube within thecrysloid or the like is attached to the front of tal may be cemented tothe crystal. Preferably, atransparent closure plate 25 of celluframe 6,forin stance by means of screw 26., an opening 27 through plate 25 beingprovided for the passage of leads-15 and 16, and

/ an opening 28-through the plate 25 being provided for the attachmentof the apex of the diaphragm to the torsion arm 12. The back of theframe is preferably closed by a plate similar to plate 25 which may,however, be of brass or the like.

The base 5 is shownas resting" upon a table top 35 or a like fixedsupport and as having one face 36 recessed as at 37 to receive the backof frame 6. The base may be, for instance, of wood or metal, and may, if

desired, be rigidly fastened to the frame, for example by screw .boltsor the like (not shown) passed through the bottom portion 38 of theframe and into the base. Breferably the face 36 .is inclined to thevertical in such a manner that, as shown in the drawing, a horizontalplane passed through the apex of the diaphragm would pass between itsaxis and the lowest point on its periphery, so that the base need not betall in order to bring the lowest part of the diaphragm higher than thelowest part of the base.

The prinicpal axis of the crystal is preferably inclined to a verticalplane passed perpendicular to the face 36 of'the base5 and through thecenter of that face, so that the frame 6 and the diapragm 8 may each besymmetrically located with respect to that lane. p

The bottom portion 38 of the frame 6',

" 6 that is, the portion nearest the lower basal reflect elastictwisting vibrations of thecrystal, so that the crystal vibrations willbe efiiciently transmitted to the diaphragm.

8 is preferably a conical.

Of course, the frame 6 and base 5 may, if desired, be one integralcasting. .If the nut 11 is cramped or tightened against the frame 6 thecrystal and its internal electrode will be more or less rigidlyconnected to-both the top and the bottom portions of the frame. Thisadjustment will increase the stiffness or elastictity of the structurecomprising the crystal and the frame and, therefore, will increase thenatural frequency of vibration of thestructure. On the other hand,easing Ifut 11 off the frame ,will tend to increase the responsivenessof the loud speaker to low frequencies.

The loud speaker. is reversible in its action, so it may also beregarded as a telephone transmitter. The gener'alprinciples hereindisclosed may be" embodied in many organizations widely different fromthose illustrated, without departing from the spirit of the invention asdefined in the appended claims.

What is claimed is: l 1. In combination,'a piezo-electric crystal, aframe therefor, means for transmitting elastic vibrations ofthe crystalto a diaphragm, and internal electrode means for the crystal, saidelectrode means protrudin through the surface of said crystal anengaging said first means and said frame.

2. In combinations, a piezo-electric crystal having side walls and end wa frame for said crystal, a member for transmitting elastic vibrationsof the crystal to a dia-- phragm, and internal electrode means for thecrystal, said means'protruding from the end walls of the crystal andrigidly attached to said frame adjacent each end of said crystal, andrigidlyattached to said arm.

3. In combination, a piezo-electric crys- R tal, a band-shaped frametherefor, a member for transmitting elastic vibrations fof the crystal-to' a diaphragm, internal electrode means for the crystal, said meansprotruding from the surface of the crystal and en- 110 gaging saidmember and said frame, and means closing the front and back of said.band-shaped frame to form a box-like en- 1 closure for said crystal.

'tal having sidewalls and end'walls, a memher at one end of said crystalfor ransmitting elastic vibrations of the crystal to a diaphragm, aframe for said crystal, said frame having a massive portion at theopposite end ,of said crystal for reacting against elastic vibrations ofsaid crystal, and internal electrode means for the crystal, said meansprotruding from the end walls of the crystal and engaging said memberand said frame. A

5. In combination, a piezo-electric crystal, a band-shaped frametherefor, a fibrous conical diaphragm having 'a free periphery, a memberfor transmitting elastic vibrations 1 of said crystal to said diaphragm,internal electrode means for said crystal, said means extending throughthe surface of the crystal and engaging said member and said frame,means closing thevfront and the back of said frame, and means extendingthrough said closure means and connecting said diaphragm and saidmember.

6. In combination, a piezo-electric crystal and a tube containing liquidfor supplying moisture to the crystal, said tube being car- 'ried by thecrystal and lying at least partly within it.

7. In combination, a' piezo-electric crystal, ,a band-shaped frametherefor, a member for transmitting elastic vibrations of the crys talto a diaphragm, means extending from the surface of the crystal andengaging said member and said-frame, means closing the front and back ofsaid band-shaped frame to form a box-like enclosure for said crystal,and fibrous material between said crystal and said enclosure.

8. In combination, a piezo-electric crystal, a frame therefor, means fortransmitting elastic vibrations of the crystal to a diaphragm, and meansprotruding through, r

the surface of the crystal andengaging said first means and said frame.

9. In combination, a piezo-electric crystal, means for-transmittingelastic vibrations of the crystal to a diaphragm, a base for thecrystal, for reflecting its elastic vibrations, and internal electrodemeans for the 'crystal, said electrode means protruding through thesurface of said crystal and being rigidly connected to said base}:

10. In combination, a piezo-elec ric crystal, a base therefor, and meansfor supporting said crystal from said base, and means comprising meanspenetrating said crystal and engagin said base. 7

11. In com ination, a piezo-electric body, a base therefor havingopposed portions, a rod-like member passing through said body and beingattached to said opposed portions, means on said member for clamplngsaid crystal to one of said portions and means adjacent said otherportion for tensioning said member. g

In witness whereof, I hereunto subscribe my name this 26 'day ofDecember A. D.,

ALEXANDER M. NICOLSONZ

